Hidden image security device and method

Abstract

A method for producing an optical device, preferably a security device, including the steps of: forming a planar relief structure on a substantially planar first surface of a substrate, preferably a transparent substrate, the planar relief structure having a first alignment direction and including a plurality of relief structure elements each having the same height; and applying a liquid crystal polymer (LCP) layer onto the planar relief structure such that the LCP layer is aligned with the relief structure, wherein the LCP layer includes at least one or more first LCP regions having a first height and one or more second LCP regions having a second height above the substantially planar first surface of the substrate, wherein the second height is different to the first height, and an optical device formed by such a method.

1 .- 58 . (canceled) 
     
     
         59 . An optical device, preferably a security device, including a relief structure formed on a substantially planar first surface of a substrate, the relief structure having a first alignment direction and including a plurality of relief structure elements and a liquid crystal polymer (LCP) layer applied to the relief structure such that the LCP layer is aligned with the relief structure, wherein the LCP layer includes at least one or more first LCP regions having a first height and a first thickness and one or more second LCP regions having a second height and a second thickness above the substantially planar first surface of the substrate, wherein the second height is different to the first height, and wherein the second thickness is different to the first thickness. 
     
     
         60 . An optical device as claimed in  claim 59 , wherein the, or each, first LCP region is associated with a first colour, and wherein the, or each, second LCP region is associated with a second colour, different to the first colour. 
     
     
         61 . An optical device as claimed in  claim 59 , further including a high refractive index (HRI) layer applied to the LCP layer. 
     
     
         62 . An optical device as claimed in  claim 61 , wherein the HRI layer extends past the edges of the LCP layer. 
     
     
         63 . An optical device as claimed in  claim 61 , wherein the HRI layer includes a substantially flat outward facing surface. 
     
     
         64 . An optical device as claimed in  claim 61 , wherein the HRI layer is selected to have a refractive index the same as, or substantially the same as, the ordinary refractive index of the LCP layer. 
     
     
         65 . An optical device claimed in  claim 61 , wherein the HRI layer is selected to have a refractive index the same as, or substantially the same as, the extraordinary refractive index of the LCP layer. 
     
     
         66 . An optical device as claimed in  claim 61 , wherein the HRI layer is selected to have a refractive index between the ordinary and extraordinary refractive indices of the LCP layer. 
     
     
         67 . An optical device as claimed in  claim 61 , wherein the HRI layer is selected to have a refractive index substantially greater than the largest refractive index of the LCP layer. 
     
     
         68 . An optical device as claimed in  claim 59 , wherein the substrate includes an embossing layer corresponding to the relief structure. 
     
     
         69 . An optical device as claimed in  claim 68 , wherein the embossing layer includes a radiation curable ink. 
     
     
         70 . An optical device as claimed in  claim 59 , wherein the liquid crystal polymer layer is applied using a printing process, preferably selected from gravure printing, intaglio printing, offset printing, silk screen printing, or inkjet printing. 
     
     
         71 . An optical device as claimed in  claim 59 , wherein each relief structure element is longitudinally extending and arranged parallel to each other. 
     
     
         72 . An optical device as claimed in  claim 59 , wherein the substrate is transparent and including a first linear polariser located on a second surface of the substrate, opposite the LCP layer. 
     
     
         73 . An optical device as claimed in  claim 72 , wherein the linear polariser has a polarising direction aligned at substantially 45 degrees with respect to the first alignment direction. 
     
     
         74 . An optical device as claimed in  claim 59 , wherein the LCP layer includes one or more structured regions, wherein the, or each, structure region includes a grating profile formed on the outward facing surface of the LCP layer. 
     
     
         75 . An optical device as claimed in  claim 74 , wherein the relief structure includes one or more non-relief regions, and wherein the structured regions are located overlapping the, or each of the, one or more non-relief regions. 
     
     
         76 . An optical device as claimed in  claim 74 , wherein the grating profile is configured to provide a diffractive effect. 
     
     
         77 . A security document, preferably a banknote, including a document substrate including an optical device according to  claim 59  in a region of the document substrate. 
     
     
         78 . A security document as claimed in  claim 77 , including a first opacifying layer applied to a side of the document substrate, the first opacifying layer including a window region such that the optical device is located in the window region. 
     
     
         79 . A security document as claimed in  claim 77 , including a polariser formed in a region of the document substrate different to the location of the optical device, such that the optical device can be viewed through the polariser by twisting, folding, or other manipulation of the document substrate. 
     
     
         80 . A method for producing an optical device, preferably a security device, including the steps of:
 a. forming a relief structure on a substantially planar first surface of a substrate, the relief structure having a first alignment direction and including a plurality of relief structure elements; and   b. applying a liquid crystal polymer (LCP) layer onto the relief structure such that the LCP layer is aligned with the relief structure,   wherein the LCP layer includes at least one or more first LCP regions having a first height and a first thickness and one or more second LCP regions having a second height and a second thickness above the substantially planar first surface of the substrate, wherein the second height is different to the first height, and wherein the second thickness is different to the first thickness.